Various methods can be used to print an image onto plastic card based media, for example security cards. One method is thermal transfer printing, of which there are generally two types: direct to card and reverse transfer. Direct to card is where images are transferred from a dye film directly into the plastic card surface. Reverse transfer is where images are transferred from a dye carrying film to a reverse transfer film in order to build up a composite image. This composite image is then transferred to, and bonded with, the plastic card in a second process.
Methods exist in creating a second image on the card in addition to the normal, or primary, printed image for direct to card printing processes. This second image is often used as a security feature, in that it provides additional assurance that the printed card is genuine. Examples of a second image include watermarks, UV images, holographic images, and optically variable devices.
However, in the field of reverse transfer printing, few methods of creating a second image are available. Of the methods watermarks, UV images, holographic images, and optically variable devices, UV images are available as part of the reverse transfer process, and this has limitations in that it's not a truly secure method, since the method may easily be copied. It is also possible to purchase specially pre-printed holographic reverse transfer film. These films are expensive to prepare to manufacture and also the piece part cost is high. They are inflexible (once you have specified your design you are stuck with it unless you order a new film design). The security of these films is also suspect, as it would only require someone to obtain a roll of the film fraudulently to be able to apply the holographic reverse transfer film. The other methods are not currently available with reverse transfer printing, and where applied have to be done to the card either at card manufacturing or by a further lamination process after card printing.
It would be advantageous to provide a method of printing a second image, such as a visual security image, within the reverse transfer printer, at the time of printing the normal, or primary, image. It would provide further benefit in being able to make that second image a secure image that cannot be readily reproduced.